If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You must register
before you can post: click the register link above to proceed. To start viewing posts,
select the forum that you want to visit from the list below.

SDS on the 7th floor of a concrete-only building.

We've recently had a client seek assistance with installing a large UPS on the 7th floor of a building that is built entirely of concrete. It's an older building and no one can seem to find any building steel what so ever. Also worth noting that this facility is in a large metropolis, 208/120V service, with a relatively high available fault current at the source. Fault current at the UPS location is much lower though.

The UPS is a separately derived system (SDS), and as such needs a GEC connection. Without building steel nearby that would already be bonded to the grounding electrode system, we're forced to get a bit more creative than we would usually need to be. There is however an existing 4/0 CU from the water pipe in the basement to the 6th floor with a ground bar that is being shared by some other equipment. Bonding to this existing down conductor seems to be our way out.

But... is there a calculation / formula for ensuring this existing 4/0 CU between the metal water pipe and the 6th floor will serve as an adequate GEC for this UPS? My concern is the length of the conductor, but without building steel there's only so much you can do. All signs seem to suggest we just use this. But it's not exactly in the vicinity of the SDS as is recommend and I'm not sure if this officially qualifies as an effective ground for a SDS. Should we run our own ground to the water pipe 7 floors below? Thoughts?

250.30(6)
(a) Common Grounding Electrode Conductor. The common
grounding electrode conductor shall be permitted to be
one of the following:
(1) A conductor of the wire type not smaller than 3/0 AWG
copper or 250 kcmil aluminum
(2) The metal frame of the building or structure that complies
with 250.52(A)(2) or is connected to the grounding
electrode system by a conductor that shall not be
smaller than 3/0 AWG copper or 250 kcmil aluminum

Go to the 6th.

The more they overthink the plumbing, the easier it is to stop up the drain